The N gene product of coliphage lambda positively regulates gene expression by suppressing terminators that cause specific termination of gene transcription. For the antitermination of transcription, N requires the products of several nus genes of the host and a nut site encoded in delta. Once RNA polymerase is altered by N at the nut site, transcription does not stop but reads through many terminators. Several types of terminators exist in lambda: N-suppressible terminators, such as tL1, that require host Rho factor and N-suppressible terminators, such as tL2, that function without Rho. Lambda encodes a third kind of terminator that N fails to suppress. The failure of N to suppress this terminator (tb2) may be achieved if this terminator is preceded by a site (nrs) that promotes the release of N from the N-modified transcription complex. This hypothesis will be tested by genetic, structural and biochemical analysis of tb2-nrs region moleculary cloned in a plasmid in between a nut site and the fa1K gene. Mutants of the site and of host will be isolated and biochemically tested. Host factor(s) required for N release will be purified by "complementation assay." The mechanism of N-mediation antitermination will be studied in vitro in a coupled transcription-translation system by measuring galactokinase whose synthesis is dependent on transcription antitermination at tL1, tL2 or tb2 terminator in the plasmid. The role of nut site and several Nus proteins will be studied. Interaction of various components of antitermination will be analyzed with purified wild type and mutant proteins. The release of N at nrs and its possible role in the catalytic action of N will be investigated.